A gas turbine engine typically includes an exhaust duct through which hot combustion gases are flowed during operation of the engine. The exhaust duct conventionally comprises an inner cylindrical member forming the inner wall of the gaspath and an outer cylindrical member forming the outer wall of the gaspath. A plurality of radially extending struts spans the gaspath between the inner and outer cylindrical members.
Hot combustion gases discharging from the turbine into the exhaust duct during operation of the engine have a residual velocity component in the tangential direction with respect to the inner annular gaspath. The tangential velocity component of the hot combustion gases is undesirable as it detracts from the momentum increase that produces a forward axial thrust in the gas turbine engine. Conversion of the tangential velocity to axial velocity increases the axial thrust produced in the mixer and is essential for optimum operation of the turbine engine.
The tangential velocity component of the flow is redirected axially by the struts of the exhaust duct. More specifically, each strut has an airfoil for axially straightening the flow, the airfoil profiles being configured so as to aerodynamically affect the turning of the flow of gases.
In an exhaust duct following a single stage low pressure (LP) turbine, and particularly where the duct has forced mixer component following it, the strut airfoil shape must remove a substantial amount of residual swirl in the flow leaving the single stage LP turbine, in order to ensure that the forced mixer component which follows can function correctly. The amount of swirl will vary from the inner to the outer annulus and from one engine operating condition to another. At altitude, the flow Reynolds Number will be such that the flow is subject to flow separation unless great care is taken in determining the airfoil profile shape. Thus, the flow regimes this type of airfoil is exposed to will vary substantially with engine operating conditions and will be subject to flow separation. Therefore, improvements in airfoil design are sought.